Analysis and representation of complex waves



ug. 5, 1947. R. K. POTTER ANALYSIS AND REPRESENTATION OF COMPLEX WAVESFiled D60. 23, 1944 VARIABLE FREQUENCY OJIILLATUR MARKING OKILLATMswwv/Ms FILTER RECTIFAER Patented Aug. 5, 1947 UNITED ST PATENT FFiflEANALYSIS AND REPRESENTATION OF COIHPLEX WAVES Ralph K. Potter,Morristown, N. .l., assignor to Bell Telephone Laboratories,

Incorporated,

New .York, N. Y., a corporation oi New York Application December 23,1944, Serial No. 569,557

9Claims. (01.179-1) filed April 14, 1942, Patent No. 2,403,997, July 16,

1946, there are disclosed method and means for producing a visual recordof complex waves in the form of a pat-tern the dimensions of which havethe sense of a frequency axis and a time axis, respectively, so thateach elemental area in the pattern is identified with a particularfrequency band and a particular time interval. The shade or density ofthe pattern varies from one elemental area to another to depict for eachsuch area the relative wave power that is found in the componentfrequency band identified with that area during the time intervalidentified with that area.

One of the objects of the present invention is to provide aspectographic representation in which variations in the power content ofthe various frequency bands are represented, otherwise than bycontinuous gradation in shade or density or the like, in a form allowingreadier and more accurate quantitative determination of the powercontent indicated in the pattern.

In accordance with a feature of the present invention a spectographicrepresentation of complex waves is constituted of a multiplicity ofdistinctly marked zones respective to different ranges of power contentwhereby the power content per- 2 quency band and each havingirregularities therein to indicate quantitatively the variations inpower content of .the corresponding frequency band.

The nature of the present invention and its various features, obiectsand advantages will appear more fully from a consideration of theembodiments illustrated in the accompanying drawings. In the drawings:

Fig. 1 illustrates a system for recording spectrographic representationsof the multizone type;

Fig. 2 illustrates the character of the representations formed by thesystem of Fig. 1;

Fig. 3 illustrates an alternative detail of the Fig. 2 system;

Fig. 4 illustrates another recording system in accordance with theinvention; and

Fig. 5 illustrates the type of record formed thereby.

taining to any particular frequency band and time can be determineddirectly 'by noting what particular zone embraces the correspondingelemental area in the representation. In accordance witha furtherfeature the aforesaid zones are distinctly marked by means of contourlines at their respective boundaries.

In accordance with another feature of the invention the complex waves tobe visually represented are subjected to frequency analysis while on thesurface on which the visual representation is to appear a dot or othermark is made, in the proper coordinate position, whenever the varyingpower content found by the analyzing means passes through any of amultiplicity of predetermined discrete values. The marks so made alignthemselves to form contour lines, each representing a particular powercontent and each defining a boundary of one of the aforementioned zones.

In accordance with another feature of the invention a, spectographicrepresentation of complex waves is formed of a multiplicity of lineseach identified with a particular component fre- In the specificembodiment of the invention illustrated in Fig. 1 the waves to berecorded in visual form are first recorded in electrically reproducibleform and then repeatedly played back into a frequency analyzer fromwhich are derived effects that control the formation of the visualrecord. It will he assumed for sake of concreteness that the waves to(be represented are speech bearing waves.

In Fig. 1 the speech bearing waves are derived from a microphone circuitl and applied through a. switch 2 to the recording coil 3 of a magneticrecorder. The latter includes an endless magnetic tape 4 which is drivencontinuously at a constant speed and upon which the speech bearing wavesare magnetically recorded. After the waves have been so recorded switch2 is thrown to its alternate position whereupon the recorded waves arerepeatedly played back or electrically reproduced over and over againinto a frequency analyzer comprising elements 5 to 8, inclusive.

The reproduced waves are transmitted through a wave amplifier 5, whichmay introduce a certain amount of frequency weighting or equalization ifdesired, to a frequency translator or modulator 6 that is supplied withbeating oscillations from an oscillator I. The position in the frequencyrange that is occupied by the translated band of speech bearing wavesappearing in the output corded waves.

The band width of the scanning filter 8 is small compared with thefrequency range occupied by the speech bearing waves and it may beassigned any of rather widely difierent values depending on theresolution desired. For high frequency resolution the band width may be20 or 45 cycles, for specific example, or if lower frequency resolutionor higher time resolution be desired the band width may be 300 cycles,for example. In any case the frequency bands selected in the course ofsuccessive reproductions may overlap each other to a considerableextent; that is, a wave component of a given frequency may be acceptedby the scanning filter during several successive reproductions, In theinterest of simplicity it may .be assumed henceforward that the filter 8has a narrow pass band capable of resolving the various harmonics of thefundamental voice frequency.

The wave output of filter 8 has a frequency approximating the meanfrequency of the filter pass band, which may be 12,000 cycles forspecific example, and its effective intensity, 1. e., its power contentor envelope amplitude, varies in the course of each reproduction inaccordance with the variations in the effective intensity of the speechwave component appearing in a respectively corresponding frequency band.It is this varying intensity that is to be shown in the visual record.

The visual recording elements include a pair of cylindrical metal drums20, 2| which carry a belt of electrosensitive facsimile paper 22, Thebelt 22 and the endless magnetic tape 4 are driven in synchronism witheach other, and any suitable means may be provided for this purpose. Forexample, a common motor 23 "may be provided as illustrated, orindividual motors with an electromechanical interlock to insure thattape 4 and belt 22 start each revolution simultaneously. Facsimile paper22 may be of a type comprising a titanium oxide recording surface and acarbon backing, such as the Teledeltos grade B" facsimile paperdeveloped by the Western Union Telegraph Company. The marking element isa stylus 24 which presses lightly against the face of the facsimilepaper 22. Marking current supplied to stylus 24 passes through thefacsimile paper to the grounded metal drum 20, and the electrothermaleffect of the marking current causes the paper to darken at the point ofcontact. The means provided for supplying and varying the markingcurrent will be described presently. The stylus 24, which may be a wirehaving a diameter of ten mils, for specific example, is drivenprogressively across the belt 22 in step with the change in thefrequency of beating oscillator I so that each position of the styluscrosswise of the belt 22 is identified with a particular frequency bandselected by the frequency analyzer. It may be attached to a travelingnut 25 that rides on a rotating threaded shaft 2 driven by motor 23. Thelinkage 21 signifies that the frequency adjustment of oscillator I iselectrically or mechanically geared with the position of stylus 24.

In view of the foregoing description of Fig. 1, it will be understoodthat in the course of each reproduction the frequency analyzer selects aparticular frequency band while the stylus 24' traverses a particularlongitudinal, or circumferential, path on paper 22. the position of thepath crosswise of the paper being preassigned to the particular selectedfrequency band. At the same time the wave output of filter 9 varies instrength in accordance with the varying power content 01 the selectedband.

The mechanism for translating the varying wave output of filter 8 intovariations in marking current includes a special cathode-ray tube l2comprising conventional means for producing the cathode ray and a row ofspaced conductive targets to which the ray may be selectively deflectedby voltages applied to ray deflecting plates l4. A rectifying device 9connected to the output circuit of scanning filter 8 is designed toproduce a unidirectional voltage that fluctuates according to theenvelope amplitude or effective intensity of the waves delivered by thescanning filter. This unidirectional voltage is applied to thedeflecting plates 14 and it is supplemented by a battery [5 whichprovides an opposing fixed biasing voltage sufiicient to deflect thecathode ray to a point just beyond one end of the row of targets I! whenthe output voltage of rectifier 9 is zero.

The electrical output of rectifier 9 is applied also through anamplifier ID to an amplifier II that is normally inoperative, orblocked, but which is rendered operative, or unblocked, under thecontrol of the cathode-ray tube l2. The targets l3 of the latter areconnected in multiple to the input circuit of direct-current amplifierl6 which delivers an unblocking voltage to amplifier ll whenever and solong as the cathode ray 1mpinges on one or another of the targets iii.In its operative, or unblocked, condition amplifier ll amplifies theeffects derived from rectifier 9 and transmits them to stylus 24 as amarking current. Although any suitable means may be employed to blockand unblock amplifier II, it may be normally blocked, as illustrated, bya negative grid biasing battery I! of sufficient voltage, and unblockedby applying an opposing biasing voltage derived from the output ofamplifier Ii.

It is to be noted that marking current is supplied to stylus 24 only asthe voltage supplied by rectifier 9 passes through one or another of amultiplicity of discrete finite values such that the cathode rayimpinges on one or another of the targets l3. and therefore also only asthe power content of the selected frequency band passes throughcorresponding predetermined values. Thus, each mark that is madesignifies a certain wave power level. What different levels of powercontent are to be so marked, depends on the spacing of the targets l3,and the spacing may be made uniform or non-uniform (logarithmic, forexample) as desired. Although only six targets have been indicated inthe drawing, it is contemplated that many more may be actually employed,depending on the use to which the visual record is to be put or thenumber and size of the amplitude steps that are to be recognized andindicated in the pattern. If the width of each target I3 is made smallin comparison with the intertarget spacing, the marks made on thefacsimile paper will for the most part be in the form of dots althougheach mark has a certain longitudinal extent that depends on the lengthof time the cathode ray remains on one of the targets. Occasionaltargets, every fifth one, forexample, may be made wider thanthe othersso that every fifth contour line will bemade up of definitely elongatedmarks and appear as a band.

Fig. 2 illustrates the character of the speech pattern produced by theFig. 1 system. The vertical, or transverse, dimension of the pattern hasthe sense of a frequency axis, as previously explained. Both thefrequency and time axes are indicated in Fig. 2. The marks pertaining toa given amplitude level align themselves to form contour lines, such as3| and 33, marking the boundary of zonal areas, such as 32 and 34.Contour lines 3| represent the first amplitude level, 33 the second,etc. As to any elemental area falling in the background area 30, it maybe said that at the frequency and time indicated by its coordinateposition the power content was below the first critical value. As to anyother elemental area, the power content at the frequency and timepertaining thereto isindicated, accurately, by the contour line whichmay happen to pass through the area or, approximately, by the zone inwhich it lies. In the latter case a substantially accurate evaluation ofpower content may be reached by interpolation: for example, if the arealies midway between two contour lines and the gradient indicated by theneighboring contour lines is substantially linear, the indicated powercontent would be midway between the values represented by the twocontour lines.

Fig. 3 illustrates a modification of a part of the Fig. 1 system inaccordance with which alternating marking current is employed. vThelatter may be derived from a local marking oscillator 40 oralternatively, by operating a switch 4|, from scanning filter 8. Themarking oscillations arein either case applied directly to the inputcircuit of amplifier I0, and their transmission to stylus 24 iscontrolled by the intermittent unblocking of amplifier II as previouslydescribed. The fluctuating voltage appearing in the output circuit ofrectifier 9 is applied only to the deflecting plates l4 and not toamplifier [0.

In accordance with a further modification of Figs. 1 and 3, amplifier His normally operative so that marking current is normally supplied tostylus 24, and it is intermittently blocked under the control of thecathode-ray tube l2. This modification, which entails a reversal of thepolarity of the grid biasing voltage derived from amplifier l8, producesa pattern in which the contour lines appear as light lines on a darkbackground.

The embodiment of the invention that is illustrated in Fig. 4 is similarin many respects to the Fig. 1 system and corresponding elements havebeen assigned the same reference characters. As in the Fig. 1 system,the speech bearing waves that are to be visually recorded are firstrecorded on a magnetic tape 4 and repeatedly placed back into thefrequency analyzer while the visual record is formed on the belt offacsimile paper 22. Where the Fig. 1 system employs a single movablestylus 24 the Fig. 4 system employs a multiplicity of fixed styli 44associated with a multiplicity of spaced targets 45 at the end of aspecial cathode-ray tube 42.

The targets 45 are closely spaced and in considerable number. Forexample, there may be 100 of them per inch or a total of 200 for a beltof facsimile paper that is about two inches wide. The number of targets,however, depends on the degree of frequency resolution desired, as willpresently appear, and a greater or lesser number may be employed asdesired. Each of the targets 45 is connected to a respective externalstylus 44 that bears on the facsimile paper 22. The construction ofcathode-ray tube 42 may conform with the disclosure and teaching of theUnited States patent to E. Bruce, No. 2,301,199, issued November 10,1942.

The control .voltage applied to deflecting plates l4 of the cathode-raytube 42 is derived in part from a potential divider 46 that is connectedacross a battery 41, and in part from rectifier 9. The movable contactorof potential divider 46 is driven -by the traveling nut 25 whichcontrols also the operating frequency of beating oscillator 'I. Thevoltage derived from potential divider 45 and supplied to deflectingplates l4 tends to drive the cathode ray from one end of the row oftargets 45 to the other while the frequency of oscillator I progressesfrom its one limiting value to the other.

' Each target 45 is therefore identified with a particular beatingfrequency and with a particular frequency band. The-change, from onereproduction to the next, in the voltage supplied by potential divider46 may be a stepped voltage change just sufficient to deflect thecathode ray to the next adjacent target or, more advantageously, to atarget several spaces removed, depending on the ratio of the number oftargets 45 to the total number of reproductions of the recorded waves.In either case the excitation of successively different targets 45, andof their connected styli 44, on successive reproductions of the wavetends to produce on the facsimile paper 22 a multiplicity oflongitudinal or circumferential lines on the facsimile paper, theposition of each such line crosswise of the paper identifying it with aparticular part of the frequency range.

The deflecting voltage concurrently supplied by rectifier 9, however,introduces local irregu larities in the visual record which serve as ameasure of the varying amplitude of the several wave components. Whileone such line is being traced during a particular reproduction of thewaves, for example, the power content of the band then selected mayincrease from zero to a certain maximum value and then return to zero;In such case the cathode ray is deflected to targets progressivelyfarther removed from the target on which it impinged initially, i. e.,the target identified with the selected band, and it then returns to theinitial target, the rate of departure and return conforming with therate of increase and decrease of the wave power content. This deflectionof the cathode ray is traced on the facsimile paper 22 by-the styliwhich the ray successively excites. The parts of the system are sodesigned that the maximum deflection produced by the output voltage ofrectifier 9 is small compared with the length of the row of targets 45.

Fig. 5 illustrates the nature of the visual record produced by the Fig.4 system. Each line is identified with a particular part of thefrequency range, as previously explained, and its departure crosswise ofthe record, 1. e., vertically in Fig. 5, from the position it occupieswhen the wave power content of its respective frequency band is zero, isa measure of the power content.. So long as the cathode ray remains ona. particular target, i. e., so long as the power content of a selectedband remains constant, the line formed on the record surface is acontinuous longitudinal line. As the ray is deflected the line Fbecomesdiscontinuous and comprises a multiplicity of laterally displaceddiscrete marks or dots each having a longitudinal extent depending onthe length of time the cathode ray impinges on the associated target.

It may be necessary or desirable in some cases, where patterns such asillustrated in Figs. 2 and 5 are to be used for quantitative measurementof power content, to take into account the frequency-transmissioncharacteristic of the recording system. Frequenc equalization orWeighting may be introduced into the system at a point either precedingor following the magnetic recorder in circuit sequence, for example,with the result that those frequency components which are relativelyattenuated thereby will appear in the pattern to have a lower relativeintensity than is actually the case. This may be corrected by adding theamount of relative attenuation to the intensity indicated in thepattern. In other cases it will sufiice to accept the indicatedintensity, understanding that it refers to the reproduced waves as theyappear at the input terminals of the frequency translator. For thedetermination of absolute, rather than relative power content, thesystem may be calibrated by use of multifrequency waves of variable,measurable intensity.

Although the present invention has been described largely in terms ofthe several embodiments set forth herein, it will be evident to thoseskilled in the art that the invention may be embodied in various otherforms within the spirit and scope of the appended claims.

What is claimed is:

1. A system for translating complex waves into a visual representationcomprising frequency analyzer means operative on said waves for derivingfrom each component frequency band an eifect individual thereto thatvaries in value in accordance'with the variations in the power contentof the respectively corresponding band, means controlled by the saidvarying derived effect for distinguishing a multiplicity ofpredetermined ranges of the value of said effect, marking stylus meansfor systematically following a multiplicity of collateral paths across asurface on which the representation is to appear, each of said pathsbeing individual to a corresponding component frequency band, and meansresponsive to said controlled means and operative on said stylus meansfor depicting in each said path the transition, from one of said rangesto another, of the value of the effect derived from the frequency bandcorresponding to each said path.

2. A system for translating complex Waves into a visual representationcomprising frequency analyzer means operative on said waves for derivingfrom each component frequency band an effect that varies in value inaccordance with the variations in the power content of the respectivelycorresponding band, means responsive during the transition of the valueof said varying derived effect from one to another of a multiplicity ofpredetermined ranges of value, stylus means for systematically followinga multiplicity of collateral paths across a surface on which therepresentation is to appear, each of said paths being individual to acorresponding different frequency band, said stylus means having amarking condition and a non-marking condition, and means controlled bysaid responsive means for altering the said condition of said stylusmeans during each said transition.

3. A combination in accordance with claim 2 in which'said last-mentionedmeans maintains said stylus means in its non-marking condition exceptduring said transitions.

4. A combination in accordance with claim 1 in which said control meanscomprises a row of spaced targets, means for producing a substantiallinertialess beam adapted to be deflected along said row of targets andmeans for varying the deflection of said beam in accordance with thevalue of said derived effect, and means actuated whenever said beamstrikes a target.

5. A system for the production of a visual representation of complexwaves in the form of a pattern the dimensions of which have the sense ofa time axis and a frequency axis, respectively, comprising a recordsurface On which the representation is to appear, stylus means movablerelative to and across said surface along a multiplicity of collateralpaths in succession, means for storing the complex waves, means forrepeatedly reproducing the stored waves, means for deriving from thereproduced waves an efiectthat varies in value, in th course of eachreproduction, as' the wave power varies in a respectively correspondingfrequency band, means sensitive to a change in the value of saidvariable effect from any one to another of a multiplicity ofpredetermined ranges of said value, and means controlled by saidlast-mentioned means for distinctively varying the marking effect ofsaid stylus means upon each such change.

6. A system for the production of a visual rep resentation of complexwaves in the form of a pattern the dimensions of which have the sense ofa time axis and a frequency axis, respectively, comprising a recordsurface on which the representation is to appear, means for marking onsaid surface, said marking means including Stylus means for followingeach of a multiplicity of collateral paths extending across saidsurface, means operative on said complex waves for deriving from each ofa multiplicity of component frequency bands an effect, individual toeach said band, that varies in value according to the variations in thewave power content of the individually corresponding band, and meansoperative on said stylus means for producing a mark in any of said pathswhenever the value of the effect individually corresponding to that pathpasses through any of a plurality of predetermined discretely differentvalues, said last-mentioned means comprising an array of spaced targetmeans and a substantially inertialess contact means variably displacedacross said array under the control of the varying value of the saidderived effects.

7. A combination in accordance with claim 6 in which said operativemeans includes a cathoderay tube having an array of spaced conductivetargets.

8. In combination with a source of complex waves, means for storing thesaid waves in reproducible form, means for repeatedly reproducing thestored waves, means for selecting successively different frequency bandsfrom said reproduced waves during corresponding successive reproductionsof the said waves, a record surface, marking stylus means, means formoving said stylus means relative to and across said record surfacerepeatedly in synchronism with the repeated reproduction of saidwaves,means operative on said stylus means for marking on said recordsurface during each reproduction the changes in power content of theselected band, said last-mentioned means including a cathode-ray tubehaving a multipliclty of targets to which the cathode ray may beselectively deflected, and means for variably deflecting said cathoderay under the control of the varying wave power appearing in theselected frequency band.

9. A system for translating complex waves into a visual representationcomprising frequency analyzer means for resolving the said waves intotheir various frequency components, means for repeatedly applying thesaid complex waves to said analyzer means, a record surface on which therepresentation is to be formed, a multiplicity of marking styli spacedapart across saidvrecord surface, means for moving said record surfacepast said styli repeatedly in synchronism with the repeated applicationof the waves to said analyzer means. a cathode-ray tube having a .ponentselected by said analyzer, and means for simultaneously deflecting saidcathode ray to an extent dependent on the frequency of the componentselected by said analyzer means.

RALPH K. POTTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Kwartin June 18, 1935 Number

